{"id":"CVE-2026-40574","aliases":["BIT-oauth2-proxy-2026-40574","GHSA-c5c4-8r6x-56w3","GO-2026-5314"],"url":"https://o3.security/vulnerability/CVE-2026-40574","summary":"OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims","details":"### Impact\n\nAn authorization bypass exists in OAuth2 Proxy as part of the `email_domain` enforcement option. An attacker may be able to authenticate with an email claim such as `attacker@evil.com@company.com` and satisfy an allowed domain check for `company.com`, even though the claim is not a valid email address.\n\nThe issue **ONLY** affects deployments that rely on `email_domain` restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. The practical risk ONLY exists in self-hosted or custom OIDC environments and federated setups where unexpected claim values can reach oauth2-proxy. Standard hosted providers that enforce valid email formatting ARE NOT effected.\n\n### Patches\nUsers should upgrade to `v7.15.2` or later once available.\n\n### Workarounds\nThe most effective workaround is to ensure the configured identity provider cannot emit malformed or attacker-controlled email claim values.","published":"2026-04-21T16:32:34.537Z","modified":"2026-10-28T02:30:54.242920849Z","cvss":{"score":6.8,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N"},"epss":{"score":0.00209,"percentile":0.11186,"asOf":"2026-08-12"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/oauth2-proxy/oauth2-proxy/v7","fixedVersion":"7.15.2"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40574.json"},{"type":"ADVISORY","url":"https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-c5c4-8r6x-56w3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40574"},{"type":"PACKAGE","url":"https://github.com/oauth2-proxy/oauth2-proxy"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:54.242920849Z"}}